The present invention relates to the reclamation of abrasive grain from vitreous bonded abrasive items such as grinding wheels and fragments thereof.
The production of vitreous bonded abrasive materials involves the mixing of abrasive grains with the components that on fusion will form a glass. This mixture may also include pore formers to ensure that the finished abrasive item is not without porosity. In some cases the glass-forming components may be replaced in whole or in part by a crushed glass or "frit". The mixture is usually cold pressed to the desired size in a mold and then placed in a furnace. As the temperature rises the glass components, (or the frit), melt and combine to form the glass which then flows over the surfaces of the grains and locates preferentially at points where adjacent grains touch or are in close proximity. At these points the glass forms bond posts linking the adjacent abrasive grains. Thus the typical vitreous bonded abrasive material comprises a large volume proportion of grains held together by a relatively small volume proportion of glass bond.
When a vitreous bonded wheel is formed the wheel is often discarded when only a fraction of the volume has been used. In addition the manufacturing process can on occasion produce products that are outside acceptable standards and the product must be rejected and sent to landfill, perhaps after having first been crushed, with all the extra expense this involves.
While this type of loss, expense and wastage is built into the manufacturing processes and is tolerated as part of the cost of doing business, as the technology going into the grain itself becomes more and more sophisticated, the value of the grain increases and the wastage becomes increasingly less acceptable.
A process has now been discovered which permits the recovery of grain from discarded vitreous-bonded abrasive materials and fragments of such materials. The process is inexpensive and makes grain recovery economically viable and reduces the amount of landfilling that needs to occur.